1. Field of Invention
The present invention relates generally to the field of well cleaning, and more specifically to modified coiled tubing apparatus and methods of using same in well cleaning operations.
2. Related Art
The ability to pump fluid while conveying tools makes wellbore cleanouts a natural application for coiled tubing (CT). During a conventional cleanout, fluid is pumped through the CT, often across a nozzle, and into the annulus, lifting solid particles to surface. Certain well types or conditions, however, make conventional cleanouts difficult or ineffective. For example, in wells where the CT outside diameter is small relative to the annulus internal diameter, it may be difficult to achieve the flow rate needed to lift particles in the annulus as the annular velocity is quite low.
In wells where conventional cleanouts are impractical, reverse circulation sometimes provides a means to lift solids to the surface. In reverse circulation, fluid at surface is pumped into the annulus, where it then flows down the well and into the CT, lifting particles in the process. Because the fluid velocity in the CT is much higher than in the annulus at the same flow rate, particles are more easily suspended and moved along. Using standard surface equipment, the particles are collected and disposed of with minimal disruption to normal well processes.
The main concern with reverse circulating is the safety risk associated with allowing fluid to flow from downhole to surface through the CT. A potential well must meet strict qualifications before a reverse cleanout is performed in order to minimize this risk. Current reversing tools are not adequate in many situations since they require either CT manipulation or pumping to return to a safe position, a hazardous situation arises if these functions are lost during the job. Also, presently known reversing tools can potentially allow hydrocarbons to flow up the CT to surface; the hydrocarbons can only be detected when they reach surface and already present a potential well control situation.
From the above it is evident that there is a need in the art for improvement in well cleaning.